1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display (LCD device) device and a driving method thereof.
2. Discussion of the Related Art
Generally, an LCD device controls the light transmittance of liquid crystal molecules according to video signals to display a picture on a liquid crystal panel. The liquid crystal panel includes liquid crystal cells arranged in a matrix. In an active matrix type liquid crystal display, a switching device is provided in each of the liquid crystal cells. As the active matrix type LCD device can actively control the switching device in each cell, it has an advantage in displaying motion pictures. For a switching device of the active matrix type liquid crystal display, a thin film transistor (hereinafter TFT) may be employed, as shown in FIG. 1
FIG. 1 shows an equivalent circuit diagram for a pixel formed in an LCD device according to the related art. As shown in FIG. 1, in a pixel of an active matrix type liquid crystal device, a gate line GL is formed to cross a data line DL, and a thin film transistor TFT for driving a liquid crystal cell Clc is formed at the crossing of the gate line GL and the data line DL. The active matrix type LCD device changes digital input video data into an analog data voltage based on a gamma reference voltage. Then, the active matrix type LCD device supplies the analog data voltage to the data line DL and, at the same time, supplies a scan pulse to the gate line GL thereby charging the liquid crystal cell Clc.
A gate electrode of the TFT is connected to the gate line GL. A source electrode of the TFT is connected to the data line DL. A drain electrode of the TFT is commonly connected to a pixel electrode and a storage capacitor Cst of the liquid crystal cell Clc. A common voltage Vcom is supplied to a common electrode in the liquid crystal cell Clc. The storage capacitor Cst is charged by the data voltage supplied from the data line DL when the TFT is turned on, thereby maintaining a voltage in the liquid crystal cell Clc in a certain level.
The TFT is turned on by a scan pulse applied to the gate line GL to form a channel between the source electrode and the drain electrode of the TFT and provides a voltage on the data line DL to the pixel electrode of the liquid crystal cell Clc. When the voltage on the data line DL is provided to the pixel electrode, liquid crystal molecules of the liquid crystal cell Clc change their arrangement, thereby modulating an incident light.
FIG. 2 shows a schematic description of an active matrix type LCD device according to the related art. Referring to FIG. 2, an active type LCD device includes an LCD device panel 110 where a plurality of data lines DL1 to DLm (m is a positive integer) and a plurality of gate lines GL1 to GLn (n is a positive integer) cross each other to define a plurality of pixel areas, liquid crystal cells Clc formed in each of the pixel areas, and thin film transistors TFTs formed at each of the crossings between the data lines DL1 to DLm and the gate lines GL1 to GLn to drive liquid crystal cells Clc, a data driver 120 to supply video data to the data lines DL1 to DLm of the LCD device panel 110, a gate driver 130 to supply scan signals to the gate lines GL1 to GLn of the LCD device panel 110, a gamma reference voltage generator 140 to generate gamma reference voltages and supplies them to the data driver 120, a backlight assembly 150 to emit light into LCD device panel 110, an inverter 160 to supply an AC voltage and current to the backlight assembly 150, a common voltage generator 170 to generate a common voltage and to supply it to a common electrode of the liquid crystal cell Clc, a gate driving voltage generator 180 to generate a gate high voltage VGH and a gate low voltage VGL and to supply them to the gate driver 130, and a timing controller 190 to control the data driver 120 and the gate driver 130.
In the liquid crystal panel 110, liquid crystal molecules are injected between two glass substrates. Data lines DL1 to DLm and gate lines GL1 to GLn are formed to perpendicularly cross each other on a lower substrate of the liquid crystal panel 110. TFTs are formed at the crossings of the data lines DL1 to DLm and the gate lines GL1 to GLn. The TFTs transfer video data from the data lines DL1 to DLm to the liquid crystal cells Clc in response to scan pulses. Gate electrodes of the TFTs are connected to the gate lines GL1 to GLn. Source electrodes of the TFTs are connected to the data lines DL1 to DLm. Drain electrodes of the TFTs are connected to pixel electrodes and storage capacitors in liquid crystal cells Clc.
A TFT is turned on in response to a scan pulse supplied to a gate line that is connected to its gate electrode among the gate lines GL1 to GLn. When the TFT is turned on, it transfers video data from one of the data lines DL1 to DLm, which is connected to its drain electrode among the data lines DL1 to DLm, to a pixel electrode in a liquid crystal cell Clc.
The data driver 120 supplies video data to the data lines DL1 to DLm in response to a data driving control signal DDC provided from the timing controller 190. More specifically, the data driver 120 samples and latches RGB digital video data provided from the timing controller 190 and changes the RGB digital video data into analog data voltages for representing a gray level in each of the liquid crystal cell Clc based on a gamma reference voltage provided from the gamma reference voltage generator 140.
The gate driver 130 generates scan pulses in response to a gate driving control signal GDC and a gate shift clock GSC provided from the timing controller 190 and sequentially supplies the scan pulses to the gate lines GL1 to GLn. The gate driver 130 determines a high level voltage and a low level voltage of each scan pulse in accordance with a gate high voltage VGH and a gate low voltage VGL provided by the timing controller 190, respectively.
The gamma reference voltage generator 140 generates positive gamma reference voltages and negative gamma reference voltages by using a high-state source voltage VDD supplied into it and outputs them to the data driver 120.
The backlight assembly 150 is disposed on the rear surface of the liquid crystal panel 110. The backlight assembly 150 emits light by using an AC voltage and current provided from the inverter 160 and supplies the light into each pixel of the liquid crystal panel 110.
The inverter 160 changes a square wave signal that is generated inside it into a chopping wave signal and compares the chopping wave signal with a DC source voltage provided from a system (not shown), then generates a burst dimming signal that is proportion to the comparison result. If the burst dimming signal is generated in response to the square wave signal inside the inverter 160, a driving integrated circuit within the inverter 160 controls generating an AC voltage and current that is supplied to the backlight assembly 150 according to the burst dimming signal.
The common voltage generator 170 generates a common voltage Vcom by using a high-state source voltage VDD provided into it and supplies the common voltage Vcom to a common electrode of a liquid crystal cell Clc formed in each pixel of the liquid crystal panel 110.
The gate driving voltage generator 180 generates a gate high voltage VGH and a gate low voltage VGL by using a high-state source voltage VDD provided into it and supplies them to the gate driver 130. The gate high voltage VGH is greater than or at least equal to a threshold voltage of a TFT formed in each pixel and the gate low voltages VGL is less than the threshold voltage of a TFT. The gate high voltage VGH and the gate low voltage VGL are used to decide a high level voltage and a low level voltage of a scan pulse generated by the gate driver 130, respectively.
The timing controller 190 receives RGB digital video data provided from a scaler (not shown) formed in a system such as a television receiver and a monitor for a personal computer, etc. and supplies the RGB digital video data the data driver 120. The timing controller 190 generates a data driving control signal DDC and a gate driving control signal GDC by using horizon/vertical synchronizing signals H and V according to a clock signal CLK, then, supplies the data driving control signal DDC and the gate driving control signal GDC to the data driver 120 and the gate driver 130, respectively. The data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarization control signal POL and a source output enable signal SOE, etc. The gate driving control signal GDC includes a gate start pulse GSP and a gate output enable signal GOE, etc.
However, because the LCD device is a hold type display device, a motion blurring phenomenon is displayed on a screen. This motion blurring phenomenon causes a motion picture to be blurred on the LCD display. This motion blurring phenomenon will be explained in conjunction with FIGS. 3 and 4, which represent a data characteristic of an LCD device and a cathode ray tube CRT.
In contrast, the CRT, as shown in FIG. 3 (a), is an impulse type display device that displays data by making a phosphorus emit light for a very short time in an early stage of one frame period and where most of the one frame period remains as a pause interval. Accordingly, in the CRT, a sharper image is perceived, as shown in FIG. 3 (b).
In a liquid crystal display, as shown in FIG. 4 (a), video data is supplied to a liquid crystal cell for a scanning period when a scan high voltage is supplied and the video data supplied to the liquid crystal cell is maintained in a non-scanning period that takes most of one frame period. Accordingly, the display picture is blurred in the liquid crystal display, as shown in FIG. 4 (b), because of a motion blurring phenomenon. The perceived image results from an integration effect of the image which temporarily lasts in an eye that follows a movement. Accordingly, even though the response speed of the LCD device is fast, an observer sees a blurred screen where a residual image of previous frames is displayed in a current frame, because of discordance between the movement of the eye and the static image of each frame. The motion blurring phenomenon deteriorates picture quality of an image displayed in a liquid crystal display.